Meshing for crash analysis

You can use the Crash Analysis context in Pre/Post to create 2D meshes that meet the specific requirements of crash analyses. Crash analyses are high-impact analyses where the energy flows through the geometry like wave propagation. To best capture the energy flow in the analysis, the mesh must be aligned with the direction of impact. This alignment is sometimes described as a good mesh flow. Additionally, because crash analyses are time-step dependent, more uniformly sized meshes, typically comprised of quadrilateral elements with a small percentage of triangular elements, help minimize the overall computation time required for the solve.

To create 2D meshes for crash analyses, select the Crash Analysis option from the Context list in the Meshing Preferences dialog box

Mesh alignment (flow)

For crash analyses, consistent mesh alignment helps ensure that a force applied to the meshed geometry travels linearly without being deflected by the shape of the elements. In the Crash Analysis context, the software optimizes the alignment or flow of 2D meshes to create better aligned, more structured 2D meshes with more uniform quadrilateral elements.

Inconsistent mesh flow	Consistent mesh flow in the Crash Analysis context

The software also tries to improve the flow of meshes around internal loops that define the boundaries of features within a face.

Mesh around features with poor mesh flow	Mesh around features with improved mesh flow

Additionally, the quadrilateral elements are more uniform, and the software tries to prevent the creation of rotated or diamond-shaped quadrilateral elements, where a single node is shared by three elements. Such elements can lead to a diversion in the energy flow of the analysis.

Diamond-shaped quadrilateral element

To help ensure better alignment of 2D meshes, use the following settings in the 2D Mesh dialog box:

• Select Paver from the Meshing Method list.

• Select the Attempt Multi-Block Decomposition check box.

• Select the Attempt Free Mapped Meshing check box.

• Select the Off - Allow Triangles option from the Attempt Quad Only list.

Automatic feature abstraction for crash analyses

When you select the CAD Curvature Abstraction check box in the 2D Mesh dialog box, the software uses an algorithm to identify and intelligently abstract certain types of features. During this process, the software:

• Identifies face clusters based on an analysis of curvature variation and CAD blends.

• Merges appropriate faces within those clusters

• Separately processes sliver faces and edges to automatically remove problematic geometry by collapsing short edges and removing very small faces.

This abstraction process results in improved meshes along features such as beads and fillets.

More structured meshes on flanges

Flanges are important features in automotive panels that typically bear high stress values. In the Crash Analysis context, the software tries to identify flanges and flange-like faces to generate better-aligned 2D meshes with more uniform quadrilateral elements in those regions.

Unstructured mesh on a flange	Structured mesh on a flange

Improved meshes along fillets

In the Crash Analysis context, the software produces more regular, structured meshes along fillets.

Skewed mesh along a fillet	Structured mesh along a fillet

Template-based meshes for body panel dimple regions

When you create a 2D mesh, the software identifies dimple regions within a model and produces a more regular mesh on those faces. Pre/Post then applies a pre-defined mesh template to generate the mesh on the dimple region. In an automotive body panel, dimples are typically circular or nearly circular faces that are characterized by a single outer loop (boundary) and higher average curvature than the neighboring faces.

Generating a regular mesh around dimples is important for an accurate analysis as these areas are often load-bearing.

Aligned mapped meshes around holes close to face boundaries

In the Crash Analysis context, the software creates creating meshes with improved overall mesh flow and better aligns meshes that include Mapped Hole type mesh controls.

• For holes located close to the outer boundaries of a face, the software rotates the layers of elements around the hole so that they are parallel with the closest face boundary.

• For holes located far from the outer boundaries of a face, the software rotates the layers of elements to align with a direction vector that the software derives based on the characteristics of the underlying face.

Mapped Hole mesh controls that are not properly aligned	Mapped Hole mesh controls that are properly aligned. Notice how the element edges at the top of each mapped layer align with the element edges along the boundary.

LS-DYNA specific Jacobian ratio for element quality

In the Crash Analysis context, you can specify a target Jacobian Ratio value for the elements that is consistent with the element quality requirements of the LS-DYNA solver. This ratio provides you with an idea of the overall distortion of an element. You can use the Jacobian Ratio check to identify when an element’s interior corner angles deviate too much from 90°. A Jacobian ratio close or equal to 1.0 is desired. The lower the ratio, the lower the quality of the element.

Where do I find it?

Crash Analysis context for 2D meshing

Application	Pre/Post
Prerequisite	A FEM file as the work part and displayed part
Menu	Preferences→Meshing

2D Mesh command

Application	Pre/Post
Prerequisite	A FEM file as the work part and displayed part
Command Finder	2D Mesh

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Meshing for crash analysis, Simcenter 3D 2021.1 Series

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